1. Field of the Invention
The present invention relates to a non-impact printer apparatus for printing characters, halftone images and the like with small pixels (dots) of variable size.
2. Description of the Prior Art
Various recording element sections or printer heads for use in dot printers that form output images with dots are known. Examples of such heads include a wire dot printer head, an electrostatic printer head, an ink-jet printer head, a thermal printer head, an LED (light emitting diode) array printer head and the like. An LED array printer head having 8 or more elements per mm as the dot generating elements is known to provide extremely high resolution. When this head is used in place of an optical scanning mechanism in a conventional electrophotographic copying machine, a printer can be realized in which an array of LED's is selectively turned on in accordance with a video signal to form an electrostatic latent image on a surface of an adjacent photosensitive recording member and a visualized image is obtained through development of the recording member and transfer of the developed image onto a transfer sheet. In a printer of this type, a portion corresponding to the "ON" LED's can be formed into a black or white image portion by changing the charging conditions or toner used for development.
In U.S. Pat. No. 4,596,995, examples of printers of the kind referred to above are described. In printers described in this apparatus, registers are provided for latching image data signals to respective LED's or recording elements to be enabled. In order to determine which register is to latch an image data signal rather complex circuitry in the form of a counter and decoder is provided to generate a signal to allow a register to latch the data from a data bus.
An improvement to this printer is described in U.S. Pat. No. 4,746,941. In the printer of this patent grey level or multibit data is furnished over a bus or a plurality of lines to the printhead. Data storage latches associated with each line and each LED selectively receive the data in response to a token bit signal shifted down a shift register. The token bit thus determines which LED the data is intended for and provides for an efficient means of providing for data distribution to the printhead. However, the printer apparatus of this patent is relatively complex and requires, in addition to the latches, comparators and counters to control the varying duration of an LED dot or pixel exposure period.
It is an object of the invention, therefore, to provide printer apparatus with a simplified circuitry for receiving and printing grey level data.